1. Field of the Invention
The invention relates to radio navigation satellite systems (RNSS) and global navigation satellite systems (GNSS), and more precisely to improving the navigation performance offered by those systems.
2. Description of the Prior Art
In radio navigation systems such as GALILEO or GPS, determining the orbits of the satellites of the constellation of positioning satellites and clock synchronization are based on processing measurements effected by terrestrial control stations. Because of the terrestrial location of these stations relative to the satellites of the constellation (which are in medium Earth orbit), it is difficult to position the satellites very accurately. Moreover, the terrestrial location of these stations rules out the detection of certain operational signal anomalies, reflected in waveform distortion (“evil waveform”), for example. The operational signals are transmitted by the positioning satellites and are intended to enable the positions of GNSS or RNSS receivers, for example GPS receivers, to be determined. Consequently, any operational signal transmission anomaly is liable to limit the navigation performance of radio navigation satellite systems.
In an attempt to improve the navigation performance of the next generations of GPS radio navigation systems, in particular the future “GPS III” version, it has been proposed to install on the positioning satellites thereof a so-called intersatellite ranging (ISR) transceiver dedicated to determining the pseudodistances between the satellites. However, those transceivers use dedicated signals that are totally different from the operational signals and therefore require specific time synchronization and calibration. This introduces additional complexity at the positioning satellite level and increases satellite fabrication costs. Furthermore, these transceivers are not able to determine operational signal transmission anomalies, as they process only dedicated signals.
Thus one particular object of the invention is to solve some or all of the problems cited above and more particularly to improve the navigation performance of radio navigation satellite systems.